Bhahaa,,,, as A-Cell has said, there is no logic.
Keep in mind too that you need to sort the dashpot spring too.
Basically the spring should be selected such that at peak torque the dashpot piston has risen to about 95 to 99% all the way up, you definitely don't want it reaching 100% before the engine reaches peak torque and you'll be loosing out a little on what the carb can do if it doesn't rise to that 95 - 99%.
After sorting the spring, then the needle can be sorted, and then check the spring suitability once again, but I'm sure that your SU man already knows this.
I have an excel program that I've had for many years now. No, I'm not nearly clever enough to have written it, it was written by A.R. who ever that person is? I think it's simply called SU Needles. It seems to be a little dated as there is certainly not the full spread of needle profiles in it, but profiles can be added fairly easy. It not only displays the needle profiles but allows you to compare profiles and it lists (extensively) 'options' starting from those that are closest match to those getting further away and where the differences are. Handy program, I use it fairly often.
I'm happy to make this available to the TMF, but I don't know how one goes about posting up a program, any pointers?
I've paid for a full working copy of WinSU, but I haven't yet received the unlock code (must chase that up), it really does appear a great little gadget. You guys who have used it, do you find that the suggestions are close enough or a good starting point?